Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $221.32   13.874%   $252.0259   $252.03   $252.05   $252.00  
  Purchase #2 $244.99   6.772%   $261.5807   $261.58   $261.60   $261.60  
  Purchase #3 $179.49   11.260%   $199.7006   $199.70   $199.70   $199.70  
  Purchase #4 $185.44   13.565%   $210.5949   $210.59   $210.60   $210.60  
  Purchase #5 $117.33   6.302%   $124.7241   $124.72   $124.70   $124.70  
  Purchase #6 $53.56   13.857%   $60.9818   $60.98   $61.00   $61.00  
  Purchase #7 $115.58   6.437%   $123.0199   $123.02   $123.00   $123.00  
  7 purchase totals = $1,117.71       $1,232.6279   $1,232.62   $1,232.65   $1,232.60